Im looking for new 40 rounders, or reliable used ones. Other than Bushmaster who makes them? I cant seem to find any at CTD or any other location.
Whats your experiance with them?

New 40 rounders will more than likely be USA or Western mags, which are not too reliable.  They usually are not marked.  Another way to test them is to see if the mag body will "flex" when you grap both ends and apply pressure downwards, like you are trying to bend a piece of steel.

The best mags are Sterlings, if you can find them.  Be prepared to pay $100+ for a mag.  Next best mags are PMI (Precision Mag Industries) mags.  They were made with the same equipment as Federal Ordnance mags, so I've been told.  The earlier mags were stamped "Precision Mag Industries" on the base plate.  Later production runs were left blank.